HVAC systems can be used to regulate the environment within an enclosed space. Typically, an air blower is used to pull air from the enclosed space into the HVAC system through ducts and push the air back into the enclosed space through additional ducts after conditioning the air (e.g., heating, cooling or dehumidifying the air). Various types of HVAC systems, such as roof top units, may be used to provide conditioned air for enclosed spaces.
Each HVAC unit typically includes a HVAC controller that directs the operation of the HVAC unit. The HVAC controller may also monitor the operation of the HVAC unit. Accordingly, the HVAC controller may respond to a reset condition and initiate a reset of the HVAC unit by, for example, generating a reset signal.
Various conditions or events may cause an HVAC controller to initiate a reset of a HVAC unit. A power on reset (POR) is example of a condition or an event that initiates a reset. Typically, a POR initiates a reset when power is applied to the HVAC controller. The POR may be used to ensure that the HVAC controller starts operating at a known address or a known state.
A scheduled reset may also initiate a reset. A scheduled reset occurs during normal operation of the HVAC unit in response to a defined condition or event. For example, a manual reset may occur when a designated button is activated (e.g., depressed or touched) for a predetermined amount of time. Other type of scheduled resets, for example, may include a hardware failure with an external clock source, a low voltage condition or an external interrupt.
Other types of conditions or events may also initiate a reset. A watchdog reset, for example, may occur due to a fault condition that may be potentially dangerous to the HVAC unit. A watchdog timer may be used to initiate a reset if a program of the HVAC controller due to some fault condition, such as a hang state, neglects to regularly service the watchdog timer. The watchdog timer may be regularly serviced by writing a service pulse thereto. The intention of a watchdog reset is to bring the HVAC controller back from a hung state into normal operation.